Electronic circuitry can be seriously affected by high voltage discharges such as produced by piezo electric gas lighters and the like. Historically electricity meters and other supply meters such as water supply meters and the like have not incorporated sensitive electronic circuitry. With the tendency towards more sophisticated metering, remote reading telemetary systems and the like, increasing use is made of sensitive electronic circuitry and if a high voltage discharge occurs in close proximity to such circuitry when the latter is operating, the resulting electrical interference can either cause the circuitry to perform incorrectly and for example switch off or switch on equipment when the reverse condition is in fact required, and in some circumstances may even cause the electronic circuitry to become partially destroyed due to electrical breakdown across sensitive semi-conductor junctions. A breakdown may occur whilst the controlled equipment is in one mode or another and should this occur when the controlled equipment is in its ON mode, the result will be that the controlled equipment may not be capable of being isolated or may be rendered inoperative, or in the case of a supply meter, may be left in the ON condition irrespective of whether prepayment has been made or not.
Unfortunately in practice electrical interference such as caused by lightning or other electrical equipment in proximity with or connected to the equipment containing the sensitive circuitry may also cause similar interference. It is in general impossible to distinguish between one electrical discharge and another which are sufficient to cause interference with sensitive electronic circuits, and clearly the detection of innocent or accidental interference should not penalise a domestic user or other person by, for example, terminating the supply on a semi-permanent basis in the event of any such discharge being detected. The present invention therefore not only deals with the problem of detecting and acting on local electrical interference but also seeks to indicate whether such interference is fraudulent.